Japanese Pat. Laying-Open No. 10-290529 discloses an electric power unit mounted to an electric vehicle. The electric power unit includes a battery, an electric circuit system such as a running motor supplied with power from the battery and an on-vehicle auxiliary machine, an inverter circuit for generating a commercial AC voltage that converts a direct-current (DC) voltage from the battery to a commercial AC voltage for application to a commercial power supply load, a cutoff switch provided between the inverter circuit and the commercial power supply load, and a leakage detecting circuit that detects a ground-fault current leaking from the battery so as to detect leakage of the electric circuit system.
In this electric power unit, upon detection of the leakage, the leakage detecting circuit stops the inverter circuit and causes the cutoff switch to operate to cut off the power supply to the commercial power supply load, without interrupting the power supply to the electric circuit system such as the running motor and the on-vehicle auxiliary machine.
In the load receiving the supply of the commercial AC voltage, a line-bypass capacitor (also referred to as a “Y-condenser” or a “Y-capacitor”) connected between a power line pair and a ground is sometimes provided, mainly for the purpose of removing noise.
In this case, if the electric power unit disclosed in Japanese Pat. Laying-Open No. 10-290529 is used to supply a commercial AC voltage to the load provided with such line-bypass capacitor, a ground on the side of the vehicle will be connected to a ground on the side of the load. This leads to a problem of a leakage current flowing from the load receiving the supply of the commercial AC voltage through the line-bypass capacitor, the ground and the leakage detecting circuit to a battery of the vehicle.